Coordination chemistry and reactivity of monomeric alkoxides and amides of magnesium and zinc supported by the diiminato ligand CH(CMeNC6H3-2,6-iPr2)2.: A comparative study

被引:354
作者
Chisholm, MH [1 ]
Gallucci, J [1 ]
Phomphrai, K [1 ]
机构
[1] Ohio State Univ, Dept Chem, Newman & Wolfrom Labs, Columbus, OH 43210 USA
关键词
D O I
10.1021/ic020148e
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The preparation and characterization of a series of closely related magnesium and zinc compounds are reported: LMg((NPr2)-Pr-i)(THF), 1; LZn((NPr2)-Pr-i), 2; LMg((OBu)-Bu-t)(THF), 3; LZn((OBu)-Bu-t), 4; and LZn(OSiPh3)(THF), 6; where L = CH-(CMeNC6H3-2,6-Pr-i(2))(2). Their dynamic solution behavior has been examined by variable-temperature NMR studies and reveals that THF reversibly dissociates in toluene-d(8) or CD2Cl2 and that exchange with free THF occurs by a dissociative process, Compounds 1-4 and 6 all initiate and subsequently sustain ring-opening polymerization (ROP) of lactides. For a related series of compounds LMX(THF)(n), where n = 1 or 0, the rate of initial ring-opening follows the order M = Mg > Zn and X = (OBu)-Bu-t > (NPr2)-Pr-i > NSi2Me6 > OSiPh3. In THF at 25 degreesC, compounds 3 and 4 polymerize 100 equiv of rac-lactide to >95% conversion in 5 and 80 min for M = Mg and Zn, respectively, and yield ca. 90% heterotactic PLA, (isi + sis tetrads). The reactions proceed faster in methylene chloride, but for M = Mg, a Bernoulian distribution of tetrads is formed from rac-lactide (3iii:2isi.sii.sis:iis) prior to trans-esterification. Polymerization of L-LA in toluene-d(8) and THF-d(8) by 3 and 4 have been studied by VT H-1 NMR spectroscopy: the resting state for zinc is proposed to be a monomeric species akin to LZn(eta(2)-OCHMeC(O)OMe), whereas the magnesium complex appears to be dimeric LMg(mu-OP)(2)MgL. None of the compounds is capable of initiating homopolymerization of propylene oxide (PO) or cyclohexene oxide (CHO), although the magnesium amide 1 effects ring-opening by allylic proton abstraction and the dimeric compound [LMg(mu-OC6H9)](2), 7, is formed. Reactions with carbon dioxide are also described, along with the characterization of (LZnO2CNPr2)-Pr-i, 8, which is shown to be inert with respect to CHO and PO at room temperature. All the compounds are hydrolytically sensitive, and LZn(mu-OH)(2)ZnL, 5, has been isolated from hydrolysis of compound 4. The crystal and molecular structures are reported for compounds 1-5, 7, and 8. These results are compared with those recently reported by Coates et al.
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页码:2785 / 2794
页数:10
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共 19 条
  • [1] [Anonymous], 1992, INT TABLES CRYSTALLO, VC
  • [2] Molecular design of single site catalyst precursors for the ring-opening polymerization of cyclic ethers and esters. 2. Can ring-opening polymerization of propylene oxide occur by a cis-migratory mechanism?
    Antelmann, B
    Chisholm, MH
    Iyer, SS
    Huffman, JC
    Navarro-Llobet, D
    Pagel, M
    Simonsick, WJ
    Zhong, WQ
    [J]. MACROMOLECULES, 2001, 34 (10) : 3159 - 3175
  • [3] REACTIONS OF MAGNESIUM HYDRIDES .3. STEREOSELECTIVE REDUCTION OF CYCLIC AND BICYCLIC KETONES BY DIALKYLAMINOMAGNESIUM HYDRIDES
    ASHBY, EC
    LIN, JJ
    GOEL, AB
    [J]. JOURNAL OF ORGANIC CHEMISTRY, 1978, 43 (08) : 1564 - 1566
  • [4] TRANSITION-METAL COORDINATION-COMPOUNDS
    BOUDJOUK, P
    SO, JH
    [J]. INORGANIC SYNTHESES, 1992, 29 : 108 - 192
  • [5] Campbell N. A., 1993, BIOLOGY, p[811, 718]
  • [6] Polymerization of lactide with zinc and magnesium β-diiminate complexes:: Stereocontrol and mechanism
    Chamberlain, BM
    Cheng, M
    Moore, DR
    Ovitt, TM
    Lobkovsky, EB
    Coates, GW
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 2001, 123 (14) : 3229 - 3238
  • [7] Single-site catalysts for ring-opening polymerization:: Synthesis of heterotactic poly(lactic acid) from rac-lactide
    Cheng, M
    Attygalle, AB
    Lobkovsky, EB
    Coates, GW
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1999, 121 (49) : 11583 - 11584
  • [8] Single-site β-diiminate zinc catalysts for the alternating copolymerization of CO2 and epoxides:: Catalyst synthesis and unprecedented polymerization activity
    Cheng, M
    Moore, DR
    Reczek, JJ
    Chamberlain, BM
    Lobkovsky, EB
    Coates, GW
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 2001, 123 (36) : 8738 - 8749
  • [9] Catalytic reactions involving C1 feedstocks:: New high-activity Zn(II)-based catalysts for the alternating copolymerization of carbon dioxide and epoxides
    Cheng, M
    Lobkovsky, EB
    Coates, GW
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1998, 120 (42) : 11018 - 11019
  • [10] Monomeric metal alkoxides and trialkyl siloxides:: (BDI)Mg(OtBu)(THF) and (BDI)Zn(OSiPh3)(THF).: Comments on single site catalysts for ring-opening polymerization of lactides
    Chisholm, MH
    Huffman, JC
    Phomphrai, K
    [J]. JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 2001, (03): : 222 - 224